More than four in 10 patients undergoing abdominal surgery at one hospital in the UK die within 30 days, according to figures described as "shocking" yesterday.

The death rate for the emergency surgery is 12 times higher than at the best performing hospital, where just one in 28 patients dies. But patients have no means of knowing which is the safer hospital, as the research does not name the trusts involved.

The findings, from the UK's first national audit of abdominal surgery, come as a separate study suggests death rates following all types of surgery are much higher than previously thought. The overall death rate after surgery in the UK is 3.6 per cent, more than double previous estimates, according to Queen Mary, University of London research in The Lancet.

Around 35,000 emergency abdominal operations are performed each year making it a common surgical procedure. Most patients are over 65 and often seriously ill with internal bleeding or a tear in the bowel wall.

Professor Mike Grocott, consultant anaesthetist at Southampton University, who is co-leading the audit, said: "These data are shocking and may reflect the wide variation in provision of care across UK hospitals, both in terms of availability of essential services and of consultant anaesthetists and surgeons who should be present to conduct these operations."

Evidence shows that death rates are lower when operations are performed by consultants and where patients have ready access to treatment in intensive care following surgery.

Professor Grocott said doctors at the hospital with the highest death rate would be aware of their poor performance and should be examining the reasons for it. But of even greater concern are hospitals that had not participated. The audit, to be presented to the annual congress of the Association of Anaesthetists today, was conducted among 1,800 patients at 35 hospitals who volunteered to submit data – leaving around 200 which did not.

"What's happening in the 200 hospitals that were not interested in collecting their data? One could speculate there may be some who are performing even worse," Professor Grocott said.

The 30-day mortality rate following abdominal surgery ranged from 3.6 per cent in the best performing hospital to 41.7 per cent in the worst. The audit was carried out at the request of surgeons and anaesthetists who said there was little data to drive improvement. Professor Grocott said it was possible the worst performing hospital treated older, sicker patients but "the magnitude of the difference is unlikely to be explained by these factors alone".

"It is very hard to understand that difference without reference to the quality of care," he added. A full audit of all hospitals performing the surgery in the UK will begin next year.